In 2005, the Supreme Court struck down the death penalty for criminals under 18, in part based on data showing that the brain is still developing up to that age. That's one example of how neuroscience is redefining the American legal system. A second is the increasing inclusion of brain scans and other neurological evidence in the courtroom. If you're a lawyer who is arguing that your client couldn't curb his aggression, says forensic neuropsychologist Daniel A. Martell, PhD, assistant clinical professor at the David Geffen School of Medicine at UCLA, "and you have a scan that says he has holes in his brain like Swiss cheese in the impulse control spot, that helps make your case. And it helps juries understand why the behavior occurred."

In capital litigation, Martell says, neurological evidence is used in practically every case—"in fact, lawyers can be found to be ineffective if they don't pursue the possibility of abnormalities in the defendant's brain. From those cases, it has kind of trickled down and is becoming more popular in more straightforward criminal trials, where it may form the basis for some sort of insanity defense."

Nita Farahany, JD, PhD, assistant professor of law and philosophy at Vanderbilt University, cites one telling case in a report she recently presented on the subject. In People v. Stokke (2007), she writes, "the defendant was charged with attempted murder, assault with a deadly weapon, and discharging a firearm with gross negligence. ... An expert on fetal alcohol spectrum disorders testified that he had reviewed the defendant's brain scans and that, beyond a reasonable doubt, the defendant suffered brain damage caused by heavy prenatal alcohol exposure." Stokke was eventually found guilty of attempted voluntary manslaughter, a lesser crime than the murder charge.

Another legal area that's getting what you might call "neurocized" is lie detection. Two companies, Cephos Corp. and No Lie MRI, are now marketing tests based on fMRIs, claiming better than 90 percent accuracy. Some experts argue, however, that applying the technology for lie detection is premature. "The problem is, there's more to a thought than blood flow and neurons calling up oxygen," says Owen D. Jones, JD, a professor of law and biological sciences at Vanderbilt, referring to how fMRIs indicate activity. "There's a big difference between how the brain thinks and what the brain thinks."

Nevertheless, researchers are rushing to find the keys to the neuro-lockbox: Both the government's Defense Advanced Research Projects Agency and NASA are funding the development of technology that could conceivably decipher someone's intentions (make a deposit, or blow up the bank?) from a distance. "I think this could have positive implications for the criminal justice system, but if it happens without transparency, it will be problematic," Farahany says. "Our expectations of privacy will have to change quite a bit."